T The Humboldt Current : the ecosystem with a range of extremes

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Sheet n°310 - January 2009
eastern part of the
Pacific Ocean, off
the coasts of Peru
and Chile. It is an
oceanic ecosystem
manifesting wide
extremes and a whole
set of paradoxes.
Its waters are turbid
brownish green in
colour. They are
particularly cold for a
tropical region (with
sea surface temperature about 16°C),
owing to a strong
phenomenon of
coastal upwelling1. It
occupies less than
0.1% of the global
ocean surface area
but is the ground for
10% of the Earth’s
fish catch. However,
the western side of
South America is
undergoing the full
impact of climatic
disturbances coming
from over the Pacific
such as the warm
El Niño and cold
La Niña events. In
a context of global
climate change, it is
crucial to understand
how this emblematic
system functions.
To further this aim,
IRD researchers and
their partners from
the Peruvian Marine
Institute (IMARPE)2
have been working
jointly since 2001 to
unravel the paradoxes
of this uniquely
operating ecosystem.
They recently
produced the first full
review of the subject
for 20 years.
© IRD/Arnaud Bertrand
he Humboldt
T
Current System
operates in the
The Humboldt Current :
the ecosystem with a range of extremes
Peruvian purse-seiners target small coastal pelagic fish like anchovy which proliferate in
the Humboldt Current .
Its waters generate the world’s most
abundant fish production. The northern part of the Humboldt Current displays exceptional biological productivity,
owing to nutrients carried up by upwelling. This ecosystem produces more
fish per unit surface area than any other
open marine space on Earth. The dynamics of the Humboldt Current System
is closely governed by that of the whole
of the tropical Pacific. More than any
other region, this large area is periodically subjected to considerable climatic stress. This is exerted in the form of
El Niño events which upset the regimes
of wind, rainfall and marine current systems over periods of several months and
also affect sea temperatures and oxygen
concentrations.
The Humboldt Current System also has
the special feature of encompassing the
most intense minimum oxygen zone3
(MOZ) in the world, and the closest to
the ocean surface. Contrary to what
was hitherto thought, the region contributes to global-scale greenhouse gas
balances, owing partly to denitrification
which takes place in the acid waters of
the MOZ.
This absence of oxygen on the ocean
floor preserves the dead organisms deposited in sediments. Investigation of
these can help reconstruct past climatic
conditions and productivity. The research
team showed that the development of
the world’s largest monospecific fishery,
that of Peruvian anchovy, coincided with
the most productive period of the past
700 years.
There is practically no oxygen in the
water column and this forces many
species to congregate massively close
to the surface. The fish sometimes have
only a dozen metres of oxygenated
water in which to live. Such situations
could worsen because the MOZs are
expanding under the impact of climate
change.
Prediction of the effects of climate variability on fish stocks and conservation
of the ecosystem they belong to are
the challenges that drive ongoing multidisciplinary research on the Humboldt
Current System.
Institut de recherche pour le développement - 44, boulevard de Dunkerque, CS 90009
F-13572 Marseille Cedex 02 - France - www.ird.fr
Retrouvez les photos de l'IRD concernant cette fiche, libres de droit pour la presse, sur www.ird.fr/indigo
CONTACTS :
ARNAUD BERTRAND
Unité mixte de recherche
Exploited Marine Ecosystems
(EME)
Adresses:
IRD - Instituto del Mar del
Perú (IMARPE)
Teruel N° 357 - Miraflores
Casilla 18-1209 - Lima 18
Perú
IRD - CRH
Av. Jean Monnet
34203 Sète cedex - France
Tel. +51 (1) 6250800
Annexe 864
[email protected]
PIERRE SOLER
Directeur du Département
Milieux et Environnement
(DME)
REFERENCES :
• Bertrand, A., Guevara, R.,
Soler, P., Csirke, J., Chavez, F. (Eds). The northern
Humboldt Current System:
ocean dynamics, ecosystem processes, and fisheries, Special Issue, Progress
in Oceanography, vol. 79, pp.
95-412, 2008.
• Chavez, F.P., Bertrand, A.,
Guevara-Carrasco, R., Soler,
P., Csirke, J. The northern
Humboldt Current System:
Brief history, present status
and a view towards the
future, Progress in Oceanography, vol. 79, pp. 95-105,
2008.
KEY WORDS :
Humboldt Current, ocean,
fisheries, climate change,
ecosystem
The paradox of the Peruvian anchovy
is a good illustration of the unexpected
way in which this ecosystem reacts to
climate variability. Anchovy have only
very limited abilities to migrate and
therefore cannot escape unfavourable
conditions. They are slow and are obliged to keep near the surface and are
easy prey for larger fish, sea lions, birds
and fishermen. How therefore can these
fish become so prolific in the waters off
Peru?
The team’s research projects revealed
that their secret lay partly in their biological and behavioural flexibility. Anchovy
tolerate a wide range of temperatures. If
conditions are hazardous, they concentrate in refuge areas. Furthermore, they
lay millions of eggs which disperse in
all directions, allowing them to explore
different environmental conditions. And
then, contrary to the theory postulating
that productivity is linked to a short food
chain, anchovy are not mainly herbivore
feeding on phytoplankton : they select
the prey that provide the most energy,
essentially large-sized animal plankton
(zooplankton).
To ensure the sustainability of fish
stocks, management strategies must
take account of the ecosystem’s different components : the populations targeted, but also their predators, prey and
competitors. However, this ecosystem
approach to fisheries management is
difficult to implement because it requires
data that are rarely collected, particularly for the non-target species.
The Humboldt Current System nevertheless lends itself well to this approach. For
45 years, IMARPE has been conducting
exemplary follow-up studies of the condi-
tions of this ecosystem. Several times
per year it runs sampling campaigns for
various species, measurements of physical, biogeochemical and fisheries data
(satellite tracking of vessels, sampling
of landings and so on). That gave the
Peruvian government the possibility of
setting in place a real-time adaptive management system, taking into account
the ecosystem components as a whole.
The Humboldt Current System is very
well documented and offers scientists
an exceptional opportunity to study
the impact of climate variability and
change on marine living resources. It
also gives a means of assessing the
adaptation capacities of marine species to environmental variability. The
system’s unique environmental characteristics open a promising window on
the future for these organisms.
Gaëlle Courcoux - DIC
Translation - Nicholas Flay
1. Upwellings are generated by winds that push
the surface waters offshore to the open ocean.
These winds drive the rising up of colder water,
laden with nutrient mineral salts, from the deeper
ocean layers along the coasts.
2. This research work is conducted jointly with
scientists from Monterey Bay Aquarium (Moss
Landing, USA) and the University of Washington
(Seattle, USA).
3. The minimum oxygen zones are areas with lowoxygen concentrations located at the eastern edges of tropical oceans, at depths between 50 and
800 m.
PRESS OFFICE :
Vincent Coronini
+33 (0)4 91 99 94 87
[email protected]
Daina Rechner
+33 (0)4 91 99 94 81
[email protected]
www.ird.fr/indigo
Offshore Peru: hauling up the net
for fish sampling, mainly anchovy.
© IRD/Arnaud Bertrand
INDIGO, IRD
PHOTO LIBRARY :
© IRD/Arnaud Bertrand
Sheet n°310 - January 2009
For further information
Birds are some of the major predators
of anchovy, along with fishermen and
sea lions.
Gaëlle Courcoux, coordinator
Délégation à l’information et à la communication
Tél. : +33 (0)4 91 99 94 90 - fax : +33 (0)4 91 99 92 28 - [email protected]
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